Recent advances in computing power and related technology have fostered the development of a new generation of powerful software applications. Gaming applications, communications applications, and multimedia applications have particularly benefited from increased processing power and clocking speeds. Indeed, once the province of dedicated, specialty workstations, many personal computing systems now have the capacity to receive, process and render multimedia objects (e.g., audio and video content). While the ability to display (receive, process and render) multimedia content has been around for a while, the ability for a standard computing system to support true multimedia editing applications is relatively new.
In an effort to satisfy this need, Microsoft Corporation introduced an innovative development system supporting advanced user-defined multimedia editing functions. An example of this architecture is presented in U.S. Pat. No. 5,913,038 issued to Griffiths and commonly owned by the assignee of the present invention, the disclosure of which is expressly incorporated herein by reference.
In the '038 patent, Griffiths introduced the an application program interface which, when exposed to higher-level development applications, enable a user to graphically construct a multimedia processing project by piecing together a collection of “filters” exposed by the interface. The interface described therein is referred to as a filter graph manager. The filter graph manager controls the data structure of the filter graph and the way data moves through the filter graph. The filter graph manager provides a set of component object model (COM) interfaces for communication between a filter graph and its application. Filters of a filter graph architecture are preferably implemented as COM objects, each implementing one or more interfaces, each of which contains a predefined set of functions, called methods. Methods are called by an application program or other component objects in order to communicate with the object exposing the interface. The application program can also call methods or interfaces exposed by the filter graph manager object.
Filter graphs work with data representing a variety of media (or non-media) data types, each type characterized by a data stream that is processed by the filter components comprising the filter graph. A filter positioned closer to the source of the data is referred to as an upstream filter, while those further down the processing chain is referred to as a downstream filter. For each data stream that the filter handles it exposes at least one virtual pin (i.e., distinguished from a physical pin such as one might find on an integrated circuit). A virtual pin can be implemented as a COM object that represents a point of connection for a unidirectional data stream on a filter. Input pins represent inputs and accept data into the filter, while output pins represent outputs and provide data to other filters. Each of the filters include at least one memory buffer, wherein communication of the media stream between filters is accomplished by a series of “copy” operations from one filter to another.
As introduced in Griffiths, a filter graph has three different types of filters: source filters, transform filters, and rendering filters. A source filter is used to load data from some source; a transform filter processes and passes data; and a rendering filter renders data to a hardware device or other locations (e.g., saved to a file, etc.). An example of a filter graph for a simplistic media rendering process is presented with reference to FIG. 1.
FIG. 1 graphically illustrates an example filter graph for rendering media content. As shown, the filter graph 100 is comprised of a plurality of filters 102-114, which read, process (transform) and render media content from a selected source file. As shown, the filter graph includes each of the types of filters described above, interconnected in a linear fashion.
Products utilizing the filter graph have been well received in the market as it has opened the door to multimedia editing using otherwise standard computing systems. It is to be appreciated, however, that the construction and implementation of the filter graphs are computationally intensive and expensive in terms of memory usage. Even the most simple of filter graphs requires and abundance of memory to facilitate the copy operations required to move data between filters. Thus, complex filter graphs can become unwieldy, due in part to the linear nature of conventional development system architecture. Moreover, it is to be appreciated that the filter graphs themselves consume memory resources, thereby compounding the issue introduced above.
Thus, what is required is a filter graph architecture which reduces the computational and memory resources required to support even the most complex of multimedia projects. Just such a solution is disclosed below.